Macromolecular Growth Requirements of Human Cells in Continuous Culture

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Abstract
Growth factors capable of promotion of prolonged cell growth of HeLa and conjunctival cells have been demonstrated in the cold ethanol fraction IV-4 of most human sera. The cells in stock culture are maintained in the minimal growth medium containing 10% dialyzed horse serum described by Eagle (Science, 1955, v. 122, 501) and modified by omission of biotin, addition of meso-inositol to 10 in[image] and substitution of Earle''s balanced salt solution by Hank''s. In the experiments, plasma fractions replaced the dialyzed horse serum. Factors which inhibited cell growth were found in the cold ethanol fraction II + III of most human sera. The effectiveness of inhibition varied from serum to serum. In general, sera containing the most effective growth factors were lowest in inhibiting factors and vice versa. When horse serum was fractionated by the same fractionating system as that employed for human serum, growth promoting factors were found in fraction II + III. No inhibiting factors were found in horse serum. Subtractions of IV-4 failed to exhibit the growth promotion of the parent fraction. Of the subtractions of II + III, III-0 (lioprotein) gave no growth inhibition. Subtractions II and III did not inhibit growth individually, but, when combined, they behaved like the parent fraction. In the growth promoting fractions of both human and horse serum, half or more of the total niacin of the original serum was present.